Corrosion barrier

ABSTRACT

A method of applying a corrosion barrier includes applying a conversion coat onto a component and applying a layer of ceramic material over the conversion coat by atomic layer deposition. The conversion coat and the ceramic material provide corrosion resistance. A component with a corrosion barrier is also disclosed.

BACKGROUND

Many aerospace components, including gas turbine engine and airmanagement system components, have corrosion barriers (coatings).Corrosion barriers improve the lifetime of the component by improvingthe corrosion resistance of the component. In particular, somecomponents have non-line of sight surfaces, such as surfaces of internalpassages or the like, which are subject to corrosion and benefit fromcorrosion barriers. In particular, crevices and small, complex featurescan serve as initiation sites for corrosion. It is difficult touniformly apply corrosion barriers to non-line of sight surfaces such asthe passages of a heat exchanger. Imperfections in the corrosion barriercan reduce its effectiveness in protecting the underlying component fromcorrosion as well as negatively impact the performance of the component.

SUMMARY

A method of applying a corrosion barrier according to an example of thepresent disclosure includes applying a conversion coat onto a componentand applying a layer of ceramic material over the conversion coat byatomic layer deposition. The conversion coat and the ceramic materialprovide corrosion resistance.

In a further embodiment according to any of the foregoing embodiments,the conversion coat is applied by dipping or tumbling.

In a further embodiment according to any of the foregoing embodiments,the ceramic material is hydrophobic or superhydrophobic.

In a further embodiment according to any of the foregoing embodiments,the ceramic material includes an element from the Lanthanide series.

In a further embodiment according to any of the foregoing embodiments,the layer of ceramic material is a first layer, and the method includesapplying a second layer of ceramic material over the first layer ofceramic material by atomic layer deposition.

In a further embodiment according to any of the foregoing embodiments,the second layer of ceramic material is hydrophobic or superhydrophobic.

In a further embodiment according to any of the foregoing embodiments,the second layer of ceramic material comprises an element from theLanthanide series.

In a further embodiment according to any of the foregoing embodiments,the layer of ceramic material includes at least one of an oxide,carbide, or nitride of at least one of aluminum, silicon, magnesium,titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc,zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, rare earthmetals (e.g., metals of the Lanthanide series), and combinationsthereof.

In a further embodiment according to any of the foregoing embodiments,the coating is applied to line of sight and non-line of sight surfacesof the component.

A method of applying a corrosion barrier according to an example of thepresent disclosure includes applying a first layer of ceramic materialonto a component by atomic layer deposition and applying a second layerof ceramic material onto the component by atomic layer deposition. Thesecond layer is hydrophobic or superhydrophobic, and the first andsecond layers of ceramic material provide corrosion resistance.

In a further embodiment according to any of the foregoing embodiments,the second layer is deposited over the first layer.

In a further embodiment according to any of the foregoing embodiments,the second layer comprises an element from the Lanthanide series.

In a further embodiment according to any of the foregoing embodiments,at least one of the first and second layers of ceramic material includesat least one of an oxide, carbide, or nitride of at least one ofaluminum, silicon, magnesium, titanium, chromium, manganese, iron,cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, hafnium,tantalum, tungsten, rare earth metals (e.g., metals of the Lanthanideseries), and combinations thereof.

In a further embodiment according to any of the foregoing embodiments,the applying is to line of sight and non-line of sight surfaces of thecomponent.

A component according to an example of the present disclosure includes abase material and a corrosion barrier. The corrosion barrier includes anactive corrosion barrier adjacent the base material and a unitary,homogenous ceramic layer over the active corrosion barrier.

In a further embodiment according to any of the foregoing embodiments,the corrosion barrier is on at least one of a line of sight surface anda non-line of sight surface of the component.

In a further embodiment according to any of the foregoing embodiments,the component is a heat exchanger.

In a further embodiment according to any of the foregoing embodiments,the ceramic layer has a thickness of between about 1 and 500 nanometers(0.00004 and 0.02 mils).

In a further embodiment according to any of the foregoing embodiments,the second ceramic layer is hydrophobic or superhydrophobic.

In a further embodiment according to any of the foregoing embodiments,the active corrosion barrier is a conversion coat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically shows an example component.

FIG. 1B schematically shows a cutaway view of the example component ofFIG. 1A.

FIG. 1C schematically shows a detail view of the example component ofFIGS. 1A-B.

FIG. 2 schematically shows an example corrosion barrier.

FIG. 3 schematically shows a method for atomic layer deposition.

FIG. 4 schematically shows another example corrosion barrier.

FIG. 5 schematically shows another example corrosion barrier.

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

DETAILED DESCRIPTION

Many aerospace components, such as gas turbine engine and air managementsystem components, have corrosion barriers. Some corrosion barriersinclude two layers—a conversion coat and a top coat. An exampleconversion coat is a chromium-containing (chromated) coat, such asPermatreat® 686A (Chemetall, Auckland, New Zealand). The conversion coatis applied by dipping or tumbling the component in the coating material,and relying on air or gravity to remove excess coating material. Exampletopcoats are silicone or phenolic epoxy coatings, such as Rockhard(Indestructible Paint, Inc., Monroe, Conn.). These topcoats can containhigh amounts of volatile organic components (VOCs), which are alsosubject to environmental regulations. The topcoats typically have athickness on the order of 5-10 microns (0.2-0.4 mils).

The application of the conversion coat and topcoats can result innon-uniform coating layers, especially on non-line of site surfaces suchas heat exchanger passages. The non-uniformity of the coating detractsfrom its ability to provide corrosion resistance. For example, jaggedirregularities in the coating can serve as nucleation cites for acidic(e.g. sulfuric acid) corrosion of the underlying component. As anotherexample, locations where the coating is deposited too thickly, forinstance drips from the gravity-driven removal of excess conversioncoating material, can cause the coating to chip away from the underlyingcomponent, leaving it exposed to a corrosive environment. The describedcoating non-uniformity can also influence the performance of theunderlying components, for example, by affecting air or fluid flowthrough heat exchanger passages.

Turning now to FIGS. 1A-C, an example component 100 is shown. In oneexample, the component 100 base material comprised of a nickel-basedmaterial, an aluminum-based material, or steel, though other materialsare contemplated.

In FIGS. 1A-C, the example component is a heat exchanger 100, though itshould be understood the following description is not limited to heatexchangers. Heat exchanger 100 includes internal features, such as ribsor fins 102 that define passages 104. The internal features 102, 104,have surfaces 106 with a corrosion barrier, as will be discussed below.The surfaces 106 are non-line of site surfaces. Heat exchanger 100 alsoincludes exterior or line of site surfaces 108. Other example componentscan have other non-line of site or line of site surfaces with thecorrosion barrier.

FIG. 2 shows corrosion barrier 200 on a surface of the heat exchanger100. The surface can be one or both of non-line of site surface 106 orline of site surfaces 108. The corrosion barrier 200 includes one layeror multiple layers, discussed in more detail below. At least one of thelayers is deposited by atomic layer deposition. In one example, anALD-deposited layer can constitute a single material, but in otherexamples, an ALD-deposited layer can constitute multiple materialsarranged in sub-layers, as will be discussed in more detail below.

FIG. 3 shows a method 300 for atomic layer deposition (ALD). In step302, a single layer of a first precursor is adsorbed onto the surface ofa component, such as the heat exchanger 100, in a reactor. In step 304,the reactor is purged of excess first precursor. In step 306, a secondprecursor is provided to the reactor, wherein the second precursor isselected to react with the adsorbed first precursor. In step 308, thereactor is purged of excess second precursor.

Adsorption of the first precursor in step 302 can be affected onnon-line of site surfaces 106 as well as line of site surfaces 108 byexposing the heat exchanger 100 to the first precursor in a reactor.Accordingly, because the first precursor is introduced and adsorbed onthe heat exchanger 100 in a single layer in step 302, and the secondprecursor reacts only with the adsorbed first precursor in step 306, theresulting deposition of material is a uniform (homogenous), continuous(unitary) layer, generally free of pinholes or other imperfections onboth line of site surfaces 108 and non-line of site surfaces 106, alonguneven or irregular areas, or areas with complex geometries. The ALDprocess can be automated, as compared to the dipping/or tumblingprocesses for the conversion coat discussed above, decreasingmanufacturing costs and time.

Steps 302-308 can be repeated to provide a layer of a desired thicknessfor the corrosion barrier 200. In one example, steps 302-308 arerepeated to provide a layer with a thickness of between about 1 and 500nanometers (0.00004 and 0.02 mils). This is an order of magnitude ormore less than the topcoat layer discussed above. As discussed above, inone example, the first and second precursors in successive repetitionsof steps 302 and 306 are the same, providing an ALD layer of a singlematerial. In another example, the first and second precursors can bechanged in successive repetitions of steps 302 and 306 to providesub-layers of different material in the ALD layer. For instance,sub-layers may be between 5 and 10 nanometers (0.0002 and 0.0004 mils)thick. In a particular example, the ALD layer comprises alternatingsub-layers of materials such as Al₂O₃ and TiO₂ (or any of the materialsdiscussed below), each of which are between 5 and 10 nanometers (0.0002and 0.0004 mils) thick, built up to an ALD layer with thickness ofbetween about 1 and 500 nanometers (0.00004 and 0.02 mils).

In one example, such as the example of FIG. 2, the corrosion barrier 200comprises the entire coating which is deposited by ALD as in method 300.In other words, the corrosion barrier 200 replaces both the conversioncoat and the topcoat discussed above. The corrosion barrier 200 providesa barrier for preventing moisture and dissolved salts from reaching thecomponent 100 and causing corrosion. The corrosion barrier 200 is arelatively thin, uniform (homogenous), and continuous (unitary) layer,even on non-line of sight surfaces of component 100. The corrosionbarrier 200 is free from volatile organic components, like the topcoatsdiscussed above. In one example, the corrosion barrier 200 is also freefrom forms of chromium which are subject to many environmentalregulations.

The corrosion barrier 200 comprises a ceramic material, such as anoxide, carbide, or nitride of aluminum, silicon, magnesium, titanium,chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium,niobium, molybdenum, hafnium, tantalum, tungsten, rare earth metals(e.g., metals of the Lanthanide series), and combinations thereof.Particular example materials are TiO₂ (titanium dioxide), Ta₂O₅(tantalum pentoxide), SiO₂ (silicon dioxide), Nb₂O₅ (niobium oxide), orAl₂O₃(aluminum oxide). The specific material is selected according tothe material of the component 100 and the operating environment of thecomponent 100. For instance, certain materials are preferred for highhumidity environments as compared to environments exposed to liquidwater. Similarly, acidic environments may require more robust materials,such as Ta₂O₅ (tantalum pentoxide) or Nb₂O₅ (niobium oxide).

FIG. 4 shows an example corrosion barrier 210 for a surface 110 of heatexchanger 100. The surface 110 can be either of the surfaces 106, 108discussed above. In the example of FIG. 4, the corrosion barrier 210includes two layers 212, 214. The first, inner, layer 212 is adjacentthe heat exchanger 100. In this example, the first layer 212 is achromium-based layer, such as the conversion coat discussed above, orcould be a chromate free conversion treatment. The second, outer layer214 comprises a ceramic material deposited by ALD such as the ALDcorrosion barrier 200 discussed above. In this example, the ALD layer214 replaces the topcoat layer discussed above, and provides a uniform(homogenous), continuous (unitary) layer over the conversion coat layer,which may not be uniform or continuous for the reasons discussed above.The conversion coat layer 212 provides an active corrosion barrier incase of damage to the ALD layer 214. The active corrosion barrier isactive in that it can undergo a chemical reaction that inhibitscorrosion. For instance, if a chromium-based active corrosion barrier isdamaged, chromate ions in a chromium-based active corrosion barrier canenter the damaged portion and react with surrounding electrolyes to formchromium oxide, which protects against corrosion. In this way, theactive corrosion barrier is “self-healing.” In other examples, thecorrosion barrier 210 comprises more than one ALD layer 214 of the sameor a different ceramic material, which is selected to provide desiredcorrosion-resistant properties to the component. In yet other examples,the topcoat layer discussed above is deposited on top of the ALD layer214 to protect the ALD layer 214 from structural or mechanical damage.In this example, the ALD layer still provides a uniform (homogenous),continuous (unitary) layer over the conversion coat layer, which may notbe uniform or continuous for the reasons discussed above.

FIG. 5 shows another example corrosion barrier 220. In this example, thecorrosion barrier 220 includes an inner ALD layer 222 and an outer ALDlayer 224. One of the inner ALD layer 222 and the outer ALD layer 224 issimilar to the ALD layers 200, 214 discussed above. The other of the ALDlayer 222 and the outer ALD layer 224 is hydrophobic orsuperhydrophobic. In one example, the hydrophobic or superhydrophobiclayer comprises an element from the Lanthanide series which imparts thehydrophobicity or superhydrophobicity to the layer. In a particularexample, the hydrophobic or superhydrophobic layer is the outer ALDlayer 224. The hydrophobicity/superhydrophobicity allows the ALD layer224 to remove moisture from the surface 110, which is particularlyimportant in preventing water buildup in small passages such as thepassages 104 (FIG. 1B-C). Furthermore, thehydrophobicity/superhydrophobicity prevents or contributes to theprevention of ice buildup. In one example, thehydrophobic/superhydrophobic layer 224 is between 1 and 10 nm (0.00004and 0.0004 mils) thick.

In another example, the corrosion barrier 210 of FIG. 4 further includesa hydrophobic or superhydrophobic outer layer in addition to theconversion coat layer 212 and the ALD layer 214. In yet another example,the ALD layer 214 in FIG. 4 is a hydrophobic or superhydrophobic layer,as discussed above.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments. In other words, corrosionbarriers comprising one or more of the various layers discussed abovewith respect to examples 200, 210, 220 is contemplated by thisdisclosure.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can be determined by studying the following claims.

What is claimed is:
 1. A method of applying a corrosion barrier,comprising: applying a conversion coat onto a component; and applying alayer of ceramic material over the conversion coat by atomic layerdeposition, wherein the conversion coat and the ceramic material providecorrosion resistance.
 2. The method of claim 1, wherein the conversioncoat is applied by dipping or tumbling.
 3. The method of claim 1,wherein the ceramic material is hydrophobic or superhydrophobic.
 4. Themethod of claim 3, wherein the ceramic material comprises an elementfrom the Lanthanide series.
 5. The method of claim 1, wherein the layerof ceramic material is a first layer, and further comprising applying asecond layer of ceramic material over the first layer of ceramicmaterial by atomic layer deposition.
 6. The method of claim 5, whereinthe second layer of ceramic material is hydrophobic or superhydrophobic.7. The method of claim 6, wherein the second layer of ceramic materialcomprises an element from the Lanthanide series.
 8. The method of claim1, wherein the layer of ceramic material comprises at least one of anoxide, carbide, or nitride of at least one of aluminum, silicon,magnesium, titanium, chromium, manganese, iron, cobalt, nickel, copper,zinc, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, rareearth metals (e.g., metals of the Lanthanide series), and combinationsthereof.
 9. The method of claim 1, wherein the coating is applied toline of sight and non-line of sight surfaces of the component.
 10. Amethod of applying a corrosion barrier, comprising: applying a firstlayer of ceramic material onto a component by atomic layer deposition;and applying a second layer of ceramic material onto the component byatomic layer deposition, wherein the second layer is hydrophobic orsuperhydrophobic, and wherein the first and second layers of ceramicmaterial provide corrosion resistance.
 11. The method of claim 10,wherein the second layer is deposited over the first layer.
 12. Themethod of claim 10, wherein the second layer comprises an element fromthe Lanthanide series.
 13. The method of claim 10, wherein at least oneof the first and second layers of ceramic material comprises at leastone of an oxide, carbide, or nitride of at least one of aluminum,silicon, magnesium, titanium, chromium, manganese, iron, cobalt, nickel,copper, zinc, zirconium, niobium, molybdenum, hafnium, tantalum,tungsten, rare earth metals (e.g., metals of the Lanthanide series), andcombinations thereof.
 14. The method of claim 10, wherein the applyingis to line of sight and non-line of sight surfaces of the component. 15.A component, comprising: a base material; and a corrosion barrier, thecorrosion barrier comprising an active corrosion barrier adjacent thebase material and a unitary, homogenous ceramic layer over the activecorrosion barrier.
 16. The component of claim 15, wherein the corrosionbarrier is on at least one of a line of sight surface and a non-line ofsight surface of the component.
 17. The component of claim 16, whereinthe component is a heat exchanger.
 18. The component of claim 15,wherein the ceramic layer has a thickness of between about 1 and 500nanometers (0.00004 and 0.02 mils).
 19. The component of claim 15,wherein the second ceramic layer is hydrophobic or superhydrophobic. 20.The component of claim 15, wherein the active corrosion barrier is aconversion coat.